1. Field of the Invention
The present invention relates to a combustion chamber for diesel engines; more particularly, it pertains to a combustion chamber for diesel engines with an inner wall which is formed at least partly of a heat-resisting material, such as ceramic material, to realize a higher operation temperature of the engine.
2. Description of the Related Art
Heretofore, there have been various proposals regarding diesel engines, which are directed to effective achievement of the improved fuel consumption, improved fuel ignitionability, increased power output, as well as clarification of the exhaust gas. Among others, such proposals include the provision of a combustion chamber into which the fuel spray is injected from an injection nozzle and of which at least the fuel-impinging area, i.e. that area of the combustion chamber inner wall which is impinged upon by the injected fuel, is formed of ceramic material or a like heat-resisting material to raise the operation temperature of the engine.
More particularly, for diesel engines in which the fuel spray is injected toward the combustion chamber inner wall, it is known to use a heat-resisting material to form the fuel-impinging area of such an inner wall. Also, for diesel engines having a piston head portion with a cavity into which the fuel spray is injected, it is similarly known to use a heat-resisting material to form at least the fuel-impinging area of the cavity. Such a state of the art is disclosed, e.g. in Japanese Utility Model Application Laid-open Publication Nos. 59-58,735; 59-111,918; 60-178,345; and 61-105,721.
However, none of the above-mentioned proposals are considered practical or a satisfactory approach, owing to the technical difficulties as follows.
First of all, due to the use of a heat-resisting material to form the fuel-impinging area of the combustion chamber inner wall, such area is maintained at a considerably high temperature during the operation of the engine. Thus, the combustion of the fuel begins prematurely, as soon as the fuel-impinging area is impinged upon by the injected fuel, so that the combustion region of the chamber is excessively heated, accompanying an increased NOx emission in the exhaust gas. These problems are still more serious when the heat-resisting material is used to form at least the fuel-impinging area on the inner wall of the cavity in the piston head, the volume of which is very small and which is thus more significantly heated.
Secondly, the ignition delay time available in the prior art arrangement is extremely shortened, so that it becomes difficult to achieve an adequate mixture of the injected fuel spray with oxygen. This results in undesirable degradation of the initial combustion property and, hence, in decreased power output as well as increased fuel consumption of the engine.